This invention relates to a draw-bending apparatus and process, and more specifically relates to a metal bending apparatus in which two spaced rotatable bending tables, which are rotatable about parallel axes, rotate through different bending angles but rotate for the same length of time.
Draw-bending apparatus is well known and commonly consists of two spaced, rotatable tables which can be clamped to respective portions of a member which is to have bends placed therein adjacent each of the tables. The tables are then arranged to rotate and to move relative to one another, so that a drawing operation and a bending operation take place simultaneously.
Where the draw-bending process need not be accurately controlled, the draw bender can be a fully mechanical device. If the draw bender must draw and bend the work material with some accuracy, the tables commonly have a hydraulically driven mechanism which may be mechanically controlled. Where exceptionally high accuracy is desired, the individual bending tables may be moved by their own respective hydraulic systems.
Draw-bending apparatus is also arranged to operate either over a large bending angle or a small bending angle. The use of one type apparatus designed for a small bending angle cannot be easily used to obtain a large bending angle without very substantial modification of the equipment. Thus, devices in their present form are not easily interchangeable with one another.
In order to limit the angle of rotation of the table of the apparatus, mechanical stops are placed in each table to define the beginning and end of the table rotation and thus define the bend radius to be placed in the workpiece. Stops were necessary since one table may continue to rotate after the other is to stop, as when the bends to be formed by the different tables have different radii. Thus, simple braking action in the operating mechanism is usually insufficient to allow the completion of the bending process with good accuracy and so that the same bending radii are always reproduced by the equipment.
The use of stops is disadvantageous, however, since it reduces the useful life of the apparatus because the bearings which carry the worktables will be stressed at each stroke and at the same point in the stroke by the high inertia parts which are in movement. Note that the braking tables are brought to a stop by stops without any prior braking deceleration. Moreover, and because of the large shock forces involved when the apparatus reaches a stop position, extremely high forces are created in the clamping arrangement between the table and the workpiece and it becomes necessary to clamp the workpiece with greater force than would otherwise be necessary to withstand the reaction forces caused by the stopping impulse forces. The necesssity to clamp the workpiece tighter than would otherwise be necessary leads to excessive and undesirable stress in the clamp area on the workpiece.
The above problems are especially apparent when the rotating tables move through different angles. This is because the tables will move at the same angular velocity so that the table with the smaller angle of rotation completes its bend and reaches its stop position before the table which has to execute a larger angle of rotation.